VDMOS (vertical diffused power MOSFET) and IGBT are two most commonly used power transistors nowadays. IGBT is composed of BJT (bipolar junction transistor) and MOS, which has the advantage of high input impedance of MOSFET and low conduction voltage drop of BJT. It is a very suitable candidate to be used in areas such as AC electric motor, frequency converter, power switch, lighting circuit, traction and driving. VDMOS is a voltage control device. Under the proper control of the gate voltage, the surface of the semiconductor is inversed and forms a conduction path. VDMOS combines the advantages of BJT and conventional MOS. Compared to BJT, it switches faster and has less switching loss. Its input impedance is high and driving power is small. It has good frequency characteristics and high linear transconductance. It should be particularly pointed out that it has a negative temperature coefficient and does not have the second-breakdown problem of BJT. It also has a larger safe operating area. Therefore, VDMOS is an ideal power device in both switching and linear applications. VDMOS has been used in different area such as motor frequency adjustment, inverter, UPS, switching power supply, electric switch, automotive electronics and electrical ballast.
Usually, VDMOS uses a traditional integrated gate area. In conduction mode, a channel is only formed at two sides of the gate area. There is a large overlap between the silicon gate and the drain electrode, namely the corresponding non-channel areas of the silicon gate and drain electrode are larger. Thus, such structure has higher Qgd. The manufacture of this traditional structure is rather complex. Six (6) or seven (7) steps of masking are needed for the whole process. Therefore, the production cost is relatively higher.
In order to improve the device performance and simplify the fabrication cost, a new planar super junction MOSFET structure is proposed.